Radio communications systems are increasingly being used for wireless communications. An example of a radio communications system is a cellular phone network. Cellular radio communications systems are wide area communications networks which utilize a frequency (channel) reuse pattern. The design and operation of an analog cellular phone system is described in an article entitled Advanced Cellular terminal Phone Service by Blecher, IEEE Transactions on Vehicular Technology, Vol. VT29, No. 2, May, 1980, pp. 238-244. The analog cellular system is also referred to as the "AMPS" system.
Recently, digital cellular phone systems have also been proposed and implemented using a Time-Division Multiple Access (TDMA) architecture. Standards have also been set by the Electronics Industries Association (EIA) and the Telecommunications Industries Association (TIA) for an American Digital Cellular (ADC) architecture which is a dual mode analog and digital system following EIA/TIA document IS-54B. Telephones which implement the IS-54B dual mode architecture are presently being marketed by the assignee of the present invention. Different standards have been promulgated for digital cellular phone systems in Europe. The European digital cellular system, also referred to as GSM, also uses a TDMA architecture.
Proposals have recently been made to expand the cellular phone system into a radio personal communications system. The radio personal communications system provides voice, digital, video and/or multimedia communications using cellular terminals. Thus, any form of information may be sent and received. Cellular terminals include a radio telephone, such as a cellular telephone, and may also include other components for voice, digital, video and/or multimedia communications.
A radio personal communications system includes at least one telephone base station, also referred to herein as a "base station". A base station is a low power transceiver which communicates with a cellular terminal such as a cellular telephone over a limited local region, such as tens of meters, and is also electrically connected to the conventional public wire telephone network. The base station allows the owner of a cellular terminal to directly access the wire telephone network when in the local region, without passing through the cellular phone network, whose access rates are typically more costly. When located outside the local region of the base station, the cellular terminal automatically communicates with the wide area cellular network at the prevailing access rates.
A major problem in implementing a radio personal communications system is security for communications between the base station and the cellular terminal. Modern cellular telephone networks include security systems and methods to prevent eavesdropping and telephone fraud. Eavesdropping may be prevented by using encryption of radio transmissions between a cellular phone and a cellular network. Fraud may be prevented by preventing radio telephone transmissions between the cellular phone and the cellular network unless identification information is successfully exchanged between the cellular phone and the cellular network. Existing cellular systems, such as the AMPS system, the ADC system and the GSM system each include their own security systems and methods. Security should not be compromised by communications between a cellular terminal and the base station of a radio personal communications system.
Security is a major concern during handover from the wide area cellular network to the telephone base station when the cellular terminal enters the local region of the telephone base station. During this handover, the telephone base station typically initiates an authentication process in order to verify that the cellular terminal is authorized to communicate with the telephone base station. If authorized, the cellular terminal is disconnected from the wide area cellular network and locked into the telephone base station. During such a handover, security must be preserved without adding excessive overhead to system performance.
A major advance in providing a secure telephone base station is described in application Ser. No. 08/205,705 filed on Mar. 3, 1994 entitled Secure Radio Personal Communication System and Method by Paul W. Dent and the present inventor Jaap Haartsen, assigned to the assignee of the present application, the disclosure of which is hereby incorporated herein by reference. In this application, the base station relays cellular verification signals between the wide area cellular network and the cellular terminal via the wire telephone network. Thus, wireless telephone calls which are routed to the cellular terminal via the base station when the cellular terminal is within the local region of the base station, may be secured by exchange of data between the cellular network and cellular terminal over the wire telephone network via the base station. Calls from the public switched telephone network which are routed through the base station can thus employ the same or similar security systems and methods which are employed by the wide area cellular network. Thus, security of communications between the cellular terminal and telephone base station is preserved. Moreover, since the same cellular verification signals are used, excess overhead during handover is reduced.
Notwithstanding the major improvement of the Dent et al. application described above, there continues to be a need for authentication/handover methods and systems for radio personal communications which preserve security of cellular communications without adding excessive overhead.